/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the
 * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.android.volley.toolbox;

import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.os.Handler;
import android.os.Looper;
import android.support.annotation.MainThread;
import android.widget.ImageView;
import android.widget.ImageView.ScaleType;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response.ErrorListener;
import com.android.volley.Response.Listener;
import com.android.volley.ResponseDelivery;
import com.android.volley.VolleyError;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

/**
 * Helper that handles loading and caching images from remote URLs.
 * <p>
 * <p>The simple way to use this class is to call {@link ImageLoader#get(String, ImageListener)} and
 * to pass in the default image listener provided by {@link ImageLoader#getImageListener(ImageView, * int, int)}. Note that all function calls to this class must be made from the main thread, and all
 * responses will be delivered to the main thread as well. Custom {@link ResponseDelivery}s which
 * don't use the main thread are not supported.
 */
public class ImageLoader
{
    /**
     * RequestQueue for dispatching ImageRequests onto.
     */
    private final RequestQueue mRequestQueue;
    
    /**
     * Amount of time to wait after first response arrives before delivering all responses.
     */
    private int mBatchResponseDelayMs = 100;
    
    /**
     * The cache implementation to be used as an L1 cache before calling into volley.
     */
    private final ImageCache mCache;
    
    /**
     * HashMap of Cache keys -> BatchedImageRequest used to track in-flight requests so that we can
     * coalesce multiple requests to the same URL into a single network request.
     */
    private final HashMap<String, BatchedImageRequest> mInFlightRequests = new HashMap<>();
    
    /**
     * HashMap of the currently pending responses (waiting to be delivered).
     */
    private final HashMap<String, BatchedImageRequest> mBatchedResponses = new HashMap<>();
    
    /**
     * Handler to the main thread.
     */
    private final Handler mHandler = new Handler(Looper.getMainLooper());
    
    /**
     * Runnable for in-flight response delivery.
     */
    private Runnable mRunnable;
    
    /**
     * Simple cache adapter interface. If provided to the ImageLoader, it will be used as an L1
     * cache before dispatch to Volley. Implementations must not block. Implementation with an
     * LruCache is recommended.
     */
    public interface ImageCache
    {
        Bitmap getBitmap(String url);
        
        void putBitmap(String url, Bitmap bitmap);
    }
    
    /**
     * Constructs a new ImageLoader.
     *
     * @param queue      The RequestQueue to use for making image requests.
     * @param imageCache The cache to use as an L1 cache.
     */
    public ImageLoader(RequestQueue queue, ImageCache imageCache)
    {
        mRequestQueue = queue;
        mCache = imageCache;
    }
    
    /**
     * The default implementation of ImageListener which handles basic functionality of showing a
     * default image until the network response is received, at which point it will switch to either
     * the actual image or the error image.
     *
     * @param view              The imageView that the listener is associated with.
     * @param defaultImageResId Default image resource ID to use, or 0 if it doesn't exist.
     * @param errorImageResId   Error image resource ID to use, or 0 if it doesn't exist.
     */
    public static ImageListener getImageListener(final ImageView view, final int defaultImageResId, final int errorImageResId)
    {
        return new ImageListener()
        {
            @Override
            public void onErrorResponse(VolleyError error)
            {
                if (errorImageResId != 0)
                {
                    view.setImageResource(errorImageResId);
                }
            }
            
            @Override
            public void onResponse(ImageContainer response, boolean isImmediate)
            {
                if (response.getBitmap() != null)
                {
                    view.setImageBitmap(response.getBitmap());
                } else if (defaultImageResId != 0)
                {
                    view.setImageResource(defaultImageResId);
                }
            }
        };
    }
    
    /**
     * Interface for the response handlers on image requests.
     * <p>
     * <p>The call flow is this: 1. Upon being attached to a request, onResponse(response, true)
     * will be invoked to reflect any cached data that was already available. If the data was
     * available, response.getBitmap() will be non-null.
     * <p>
     * <p>2. After a network response returns, only one of the following cases will happen: -
     * onResponse(response, false) will be called if the image was loaded. or - onErrorResponse will
     * be called if there was an error loading the image.
     */
    public interface ImageListener extends ErrorListener
    {
        /**
         * Listens for non-error changes to the loading of the image request.
         *
         * @param response    Holds all information pertaining to the request, as well as the bitmap
         *                    (if it is loaded).
         * @param isImmediate True if this was called during ImageLoader.get() variants. This can be
         *                    used to differentiate between a cached image loading and a network image loading in
         *                    order to, for example, run an animation to fade in network loaded images.
         */
        void onResponse(ImageContainer response, boolean isImmediate);
    }
    
    /**
     * Checks if the item is available in the cache.
     *
     * @param requestUrl The url of the remote image
     * @param maxWidth   The maximum width of the returned image.
     * @param maxHeight  The maximum height of the returned image.
     * @return True if the item exists in cache, false otherwise.
     */
    public boolean isCached(String requestUrl, int maxWidth, int maxHeight)
    {
        return isCached(requestUrl, maxWidth, maxHeight, ScaleType.CENTER_INSIDE);
    }
    
    /**
     * Checks if the item is available in the cache.
     * <p>
     * <p>Must be called from the main thread.
     *
     * @param requestUrl The url of the remote image
     * @param maxWidth   The maximum width of the returned image.
     * @param maxHeight  The maximum height of the returned image.
     * @param scaleType  The scaleType of the imageView.
     * @return True if the item exists in cache, false otherwise.
     */
    @MainThread
    public boolean isCached(String requestUrl, int maxWidth, int maxHeight, ScaleType scaleType)
    {
        Threads.throwIfNotOnMainThread();
        String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight, scaleType);
        return mCache.getBitmap(cacheKey) != null;
    }
    
    /**
     * Returns an ImageContainer for the requested URL.
     * <p>
     * <p>The ImageContainer will contain either the specified default bitmap or the loaded bitmap.
     * If the default was returned, the {@link ImageLoader} will be invoked when the request is
     * fulfilled.
     *
     * @param requestUrl The URL of the image to be loaded.
     */
    public ImageContainer get(String requestUrl, final ImageListener listener)
    {
        return get(requestUrl, listener, /* maxWidth= */ 0, /* maxHeight= */ 0);
    }
    
    /**
     * Equivalent to calling {@link #get(String, ImageListener, int, int, ScaleType)} with {@code
     * Scaletype == ScaleType.CENTER_INSIDE}.
     */
    public ImageContainer get(String requestUrl, ImageListener imageListener, int maxWidth, int maxHeight)
    {
        return get(requestUrl, imageListener, maxWidth, maxHeight, ScaleType.CENTER_INSIDE);
    }
    
    /**
     * Issues a bitmap request with the given URL if that image is not available in the cache, and
     * returns a bitmap container that contains all of the data relating to the request (as well as
     * the default image if the requested image is not available).
     * <p>
     * <p>Must be called from the main thread.
     *
     * @param requestUrl    The url of the remote image
     * @param imageListener The listener to call when the remote image is loaded
     * @param maxWidth      The maximum width of the returned image.
     * @param maxHeight     The maximum height of the returned image.
     * @param scaleType     The ImageViews ScaleType used to calculate the needed image size.
     * @return A container object that contains all of the properties of the request, as well as the
     * currently available image (default if remote is not loaded).
     */
    @MainThread
    public ImageContainer get(String requestUrl, ImageListener imageListener, int maxWidth, int maxHeight, ScaleType scaleType)
    {
        // only fulfill requests that were initiated from the main thread.
        Threads.throwIfNotOnMainThread();
        final String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight, scaleType);
        // Try to look up the request in the cache of remote images.
        Bitmap cachedBitmap = mCache.getBitmap(cacheKey);
        if (cachedBitmap != null)
        {
            // Return the cached bitmap.
            ImageContainer container = new ImageContainer(cachedBitmap, requestUrl, /* cacheKey= */ null, /* listener= */ null);
            imageListener.onResponse(container, true);
            return container;
        }
        // The bitmap did not exist in the cache, fetch it!
        ImageContainer imageContainer = new ImageContainer(null, requestUrl, cacheKey, imageListener);
        // Update the caller to let them know that they should use the default bitmap.
        imageListener.onResponse(imageContainer, true);
        // Check to see if a request is already in-flight or completed but pending batch delivery.
        BatchedImageRequest request = mInFlightRequests.get(cacheKey);
        if (request == null)
        {
            request = mBatchedResponses.get(cacheKey);
        }
        if (request != null)
        {
            // If it is, add this request to the list of listeners.
            request.addContainer(imageContainer);
            return imageContainer;
        }
        // The request is not already in flight. Send the new request to the network and
        // track it.
        Request<Bitmap> newRequest = makeImageRequest(requestUrl, maxWidth, maxHeight, scaleType, cacheKey);
        mRequestQueue.add(newRequest);
        mInFlightRequests.put(cacheKey, new BatchedImageRequest(newRequest, imageContainer));
        return imageContainer;
    }
    
    protected Request<Bitmap> makeImageRequest(String requestUrl, int maxWidth, int maxHeight, ScaleType scaleType, final String cacheKey)
    {
        return new ImageRequest(requestUrl, new Listener<Bitmap>()
        {
            @Override
            public void onResponse(Bitmap response)
            {
                onGetImageSuccess(cacheKey, response);
            }
        }, maxWidth, maxHeight, scaleType, Config.RGB_565, new ErrorListener()
        {
            @Override
            public void onErrorResponse(VolleyError error)
            {
                onGetImageError(cacheKey, error);
            }
        });
    }
    
    /**
     * Sets the amount of time to wait after the first response arrives before delivering all
     * responses. Batching can be disabled entirely by passing in 0.
     *
     * @param newBatchedResponseDelayMs The time in milliseconds to wait.
     */
    public void setBatchedResponseDelay(int newBatchedResponseDelayMs)
    {
        mBatchResponseDelayMs = newBatchedResponseDelayMs;
    }
    
    /**
     * Handler for when an image was successfully loaded.
     *
     * @param cacheKey The cache key that is associated with the image request.
     * @param response The bitmap that was returned from the network.
     */
    protected void onGetImageSuccess(String cacheKey, Bitmap response)
    {
        // cache the image that was fetched.
        mCache.putBitmap(cacheKey, response);
        // remove the request from the list of in-flight requests.
        BatchedImageRequest request = mInFlightRequests.remove(cacheKey);
        if (request != null)
        {
            // Update the response bitmap.
            request.mResponseBitmap = response;
            // Send the batched response
            batchResponse(cacheKey, request);
        }
    }
    
    /**
     * Handler for when an image failed to load.
     *
     * @param cacheKey The cache key that is associated with the image request.
     */
    protected void onGetImageError(String cacheKey, VolleyError error)
    {
        // Notify the requesters that something failed via a null result.
        // Remove this request from the list of in-flight requests.
        BatchedImageRequest request = mInFlightRequests.remove(cacheKey);
        if (request != null)
        {
            // Set the error for this request
            request.setError(error);
            // Send the batched response
            batchResponse(cacheKey, request);
        }
    }
    
    /**
     * Container object for all of the data surrounding an image request.
     */
    public class ImageContainer
    {
        /**
         * The most relevant bitmap for the container. If the image was in cache, the Holder to use
         * for the final bitmap (the one that pairs to the requested URL).
         */
        private Bitmap mBitmap;
        
        private final ImageListener mListener;
        
        /**
         * The cache key that was associated with the request
         */
        private final String mCacheKey;
        
        /**
         * The request URL that was specified
         */
        private final String mRequestUrl;
        
        /**
         * Constructs a BitmapContainer object.
         *
         * @param bitmap     The final bitmap (if it exists).
         * @param requestUrl The requested URL for this container.
         * @param cacheKey   The cache key that identifies the requested URL for this container.
         */
        public ImageContainer(Bitmap bitmap, String requestUrl, String cacheKey, ImageListener listener)
        {
            mBitmap = bitmap;
            mRequestUrl = requestUrl;
            mCacheKey = cacheKey;
            mListener = listener;
        }
        
        /**
         * Releases interest in the in-flight request (and cancels it if no one else is listening).
         * <p>
         * <p>Must be called from the main thread.
         */
        @MainThread
        public void cancelRequest()
        {
            Threads.throwIfNotOnMainThread();
            if (mListener == null)
            {
                return;
            }
            BatchedImageRequest request = mInFlightRequests.get(mCacheKey);
            if (request != null)
            {
                boolean canceled = request.removeContainerAndCancelIfNecessary(this);
                if (canceled)
                {
                    mInFlightRequests.remove(mCacheKey);
                }
            } else
            {
                // check to see if it is already batched for delivery.
                request = mBatchedResponses.get(mCacheKey);
                if (request != null)
                {
                    request.removeContainerAndCancelIfNecessary(this);
                    if (request.mContainers.size() == 0)
                    {
                        mBatchedResponses.remove(mCacheKey);
                    }
                }
            }
        }
        
        /**
         * Returns the bitmap associated with the request URL if it has been loaded, null otherwise.
         */
        public Bitmap getBitmap()
        {
            return mBitmap;
        }
        
        /**
         * Returns the requested URL for this container.
         */
        public String getRequestUrl()
        {
            return mRequestUrl;
        }
    }
    
    /**
     * Wrapper class used to map a Request to the set of active ImageContainer objects that are
     * interested in its results.
     */
    private static class BatchedImageRequest
    {
        /**
         * The request being tracked
         */
        private final Request<?> mRequest;
        
        /**
         * The result of the request being tracked by this item
         */
        private Bitmap mResponseBitmap;
        
        /**
         * Error if one occurred for this response
         */
        private VolleyError mError;
        
        /**
         * List of all of the active ImageContainers that are interested in the request
         */
        private final List<ImageContainer> mContainers = new ArrayList<>();
        
        /**
         * Constructs a new BatchedImageRequest object
         *
         * @param request   The request being tracked
         * @param container The ImageContainer of the person who initiated the request.
         */
        public BatchedImageRequest(Request<?> request, ImageContainer container)
        {
            mRequest = request;
            mContainers.add(container);
        }
        
        /**
         * Set the error for this response
         */
        public void setError(VolleyError error)
        {
            mError = error;
        }
        
        /**
         * Get the error for this response
         */
        public VolleyError getError()
        {
            return mError;
        }
        
        /**
         * Adds another ImageContainer to the list of those interested in the results of the
         * request.
         */
        public void addContainer(ImageContainer container)
        {
            mContainers.add(container);
        }
        
        /**
         * Detaches the bitmap container from the request and cancels the request if no one is left
         * listening.
         *
         * @param container The container to remove from the list
         * @return True if the request was canceled, false otherwise.
         */
        public boolean removeContainerAndCancelIfNecessary(ImageContainer container)
        {
            mContainers.remove(container);
            if (mContainers.size() == 0)
            {
                mRequest.cancel();
                return true;
            }
            return false;
        }
    }
    
    /**
     * Starts the runnable for batched delivery of responses if it is not already started.
     *
     * @param cacheKey The cacheKey of the response being delivered.
     * @param request  The BatchedImageRequest to be delivered.
     */
    private void batchResponse(String cacheKey, BatchedImageRequest request)
    {
        mBatchedResponses.put(cacheKey, request);
        // If we don't already have a batch delivery runnable in flight, make a new one.
        // Note that this will be used to deliver responses to all callers in mBatchedResponses.
        if (mRunnable == null)
        {
            mRunnable = new Runnable()
            {
                @Override
                public void run()
                {
                    for (BatchedImageRequest bir : mBatchedResponses.values())
                    {
                        for (ImageContainer container : bir.mContainers)
                        {
                            // If one of the callers in the batched request canceled the
                            // request
                            // after the response was received but before it was delivered,
                            // skip them.
                            if (container.mListener == null)
                            {
                                continue;
                            }
                            if (bir.getError() == null)
                            {
                                container.mBitmap = bir.mResponseBitmap;
                                container.mListener.onResponse(container, false);
                            } else
                            {
                                container.mListener.onErrorResponse(bir.getError());
                            }
                        }
                    }
                    mBatchedResponses.clear();
                    mRunnable = null;
                }
            };
            // Post the runnable.
            mHandler.postDelayed(mRunnable, mBatchResponseDelayMs);
        }
    }
    
    /**
     * Creates a cache key for use with the L1 cache.
     *
     * @param url       The URL of the request.
     * @param maxWidth  The max-width of the output.
     * @param maxHeight The max-height of the output.
     * @param scaleType The scaleType of the imageView.
     */
    private static String getCacheKey(String url, int maxWidth, int maxHeight, ScaleType scaleType)
    {
        return new StringBuilder(url.length() + 12).append("#W").append(maxWidth).append("#H").append(maxHeight).append("#S").append(scaleType.ordinal()).append(url).toString();
    }
}
